Ultrasound is becoming ever more accessible to biochemists and biophysicists, for studying fast reactions, and to physicians, for medical diagnostic and therapeutic purposes. However, the physical mechanisms of interaction of ultrasound and biological media are poorly understood and it is essential that these be elucidated for the safe and efficacious employment of these techniques. The objective of the proposed research is detailed study of the acoustic properties of biological media. Chief among these properties are ultrasonic absorption and velocity dispersion in mammalian tissues and in solutions of biomacromolecules. The ultrasonic absorption coefficient of tissues is treated by the transient thermoelectric method and the absorption and velocity dispersion properties of solutions is determined by various pulse techniques, depending upon frequency range, magnitude of the absorption, etc. The elastic properties of living materials are also investigated.